As a system for controlling motion of a vehicle having a single front wheel and right and left wheels that are located on a rear side of the front wheel, conventionally, there has been a technique relating to a control of turning motion of the vehicle, as disclosed in below-identified Patent Document 1. In recent years, there has been studied also a vehicle having, in addition to the three wheels, a single rear wheel located on a rear side of the right and left wheels, as disclosed in below-identified Patent Document 2.